1. Field of the Invention
This invention relates to novel aqueous quenching fluids. More particularly, it is concerned with aqueous macromolecular quenching agents characterized by excellent metal hardenabilities.
2. Description of the Prior Art
Heretofore, mineral quenching oil have widely been used as the metal quenching agent. As the mineral oil quenching is very slow in rate of metal quenching, it is distinctly characterized by causing neither quenching crack nor strain in the product. On the other hand, it is a disadvantage of mineral oil that hardening is difficult due to slow rate of quenching metals. Moreover, it is a remarkable disadvantage that as the oil is attached to the surface of metals during the quenching complicated procedures for removing the attached oil are necessary.
In order to overcome these disadvantages of mineral quenching oil a variety of aqueous quenching agents have been developed. Representative of the aqueous quenching agents are aqueous polyvinyl alcohol solutions and aqueous polyalkylene glycol solutions such as those of polyethylene glycol, polypropylene glycol and polyoxyethylenepolyoxypropylene glycol. These aqueous quenching agents are capable of rapid metal quenching as well as of satisfactory hardening. Besides, it is unnecessary or very easy to remove the material attached to the metal surface after the quenching. However, these aqueous quenching agents are disadvantageous in that quenching crack is not satisfactorily prevented and, in some cases, quenching strain is produced. It is also disadvantageous that, with aqueous quenching agents of a low solute concentration such as polyvinyl alcohol, metal quenching is greatly influenced by liquid temperature. Moreover, with aqueous quenching agents with a high solute concentration such as of polyalkylene glycols, it is necessary in order to prevent quenching crack to employ the expensive solute at a high concentration.